A person who is considered to be of below average intelligence who does things to follow the majority. Typically thought of as being unable to think or make decisions for themself, they resort to doing things because someone told them to.

"Mike is such a piss ant. He only likes that because mommy and daddy do."

Any of a number of ants that can be found indoors. So-named because they make your fingers smell like micturition (piss) when you squish them. The odour comes primarily from formic acid in the insect's body that is released when you kill it by smashing it between your fingers or squish it between your finger and a wall, sink, floor, etc.

I just killed three dozen piss ants in my bathroom lavatory! Now my fingers stink like piss!!! :-O